SUMMARY OF INVENTION
The present invention relates to high energy density electric cells in which the negative active material is lithium and the positive active material is a salt or an oxide of silver.
Such cells are already described, e.g., in U.S. Pat. No. 3,853,627 and in U.S. Pat. application No. 719,113.
Because of the insolubility of silver salts in electrolyte solvents (in particular in esters such as carbonates or sulphites), the positive electrode becomes polarized to some degree during the discharge which increases the impedance of the cell at the end of discharge.
Preferred embodiments of the present invention have among their objects the reduction of this drawback.
The present invention provides an electric cell having lithium as its negative active material, a silver salt or silver oxide as its positive active material and a solution comprising one solute and at least two solvents as its electrolyte the first of the solvents being chosen from a group of esters, and the second solvent of the electrolyte being an aromatic hydrocarbon.
In such a cell, the polarization of the positive electrode is much reduced and hence the discharge voltage is more constant than in a cell made according to the prior art.
Toluene and ortho-, meta- or para-xylene are among the aromatic hydrocarbon derivatives which are used with success.
According to one embodiment, the ester is a carbonate, e.g., propylene carbonate, ethylene carbonate or dimethyl carbonate and in this case the solute is advantageously lithium perchlorate.
According to another embodiment, the ester is a sulphite, e.g., dimethyl sulphite, propylene sulphite, propylene glycol sulphite, ethylene glycol sulphite and vinylene sulphite. In this case, lithium hexafluoroarsenate can advantageously be used as a solute.